Purification of alcohols



Feb. 16, 1932. R. M. lsHAM PURIFICATION lOF ALCOHOLS Filed July so. 1927kwa/4701.

ROBERT M /HM Patented F eb. 16, 1932 UNITEDI STATES YaA'rEN'r ori-ICEROBERT I. ISHAM, OF OXMULGEE, OKLAHOMA, ASBIGNOB T DOHEBTY RESEARCH COI-PAINY, OF YORK', N. Y., A CORPIORATION 0F DELAWARE t PUBIFICATION 0FALCOHOLS Application led July 30,

The present invention relates to the purification of alcohols.

^ The manufacture of secondary alcohols from olefines has become wellestablished.

The most important steps of the usual method for producing secondaryalcohols from oleines are the absorption of the olefines in sulphuricacid, the hydrolyzation of the resulting alkyl sulphates, and the'separation of the alcohols from the dilute sulphuric acid bydistillation. 1

Usually the alcohols obtained from the hydrolyzed mixture are rectifiedto obtain cuts corresponding to the different secondary alcohols.

It has been found, however, that some of the olefines occurring in gasesobtained by cracking oil are converted by the said process not intosecondary alcohols, but into tertiary alcohols. For instanceiso-butylene is converted into tertiary butyl alcohol. The ter- `tiaryalcohols dissolve in the secondary alcohols formed by said process anddeprcciate their value. For certain purposes itis required that thesecondary alcohols be free from tertiary alcohols. It is difficult toseparate tertiary alcohols from secondary alcohols by distillationbecause the boilingl point of tertiary butyl alcohol is almost the sameas that of secondary propyl or iso-propyl alcohol.

The principal object of the present invention is to provide a processwhereby tertiary alcohols may be effectively removed from a mixture ofalcohols.

The present invention is based on the discovery that tertiary alcoholsare more readily dehydrated than other alcohols, particularly secondaryalcohols.

I have found that secondary alcohols can be purified from tertiaryalcohols by dehydrating the tertiary alcohols. The tertiary alcoholswhen dehydrated are converted into oleiines and water, the olefinesdissolving in the secondary alcohols. The secondary alcohols can,however, be readily removed from the dissolved olefines by heating undersuitable conditions, secondary alcohols free from tertiary alcoholsthereby being produced. At temperatures below 200 C. the tertiary alco-1927. serial no. sono?. l

hols break down so slowly that the process is not commercial unless aver active catalyst is available. Preferably the ehydration ofthetertiary alcohols is carried out at about 250 C. in the presence of acatalyst which does not cause dehydration of secondary yalcohols at thistemperature. very little if an polymerization of the olefines occurs.owever, any olymers so formed are comparatively high boiling compoundsand are separated readily from the secondary alcohols in which theydissolve by rectification. If the tertiary alcohol secondary alcoholmixture is subjected to strongly dehydrating conditions, some of thesecondary alcohol is dehydrated at the same time as the tertiaryalcohol. However, the destruction of secondary alcohols does not occurat temperature of 250 C. or below unless a very active catalyst is used.In such a case, the temperature is maintained a convenient degree belowthe point at which the secondary alcohols begin to break down.

The olefines formed from the tertiary alcohols by dehydration are, asmentioned above, first dissolved in and then removed from the secondaryalcohols by rectification with a reflux condenser. These olefines comeofi' from the reflux condenser in substantially pure vapor-ous form. Itis preferred according to the present invention toy utilize theseolefines to form tertiary alcohols. As the tertiary olefines areavailable in uncontaminated condition, they form a basis for themanufacture of cheap commercially pure tertiary alcohols by absorbingthe olelines in cool sulphuric acid. hydrolyzing the resulting alkylsulphates and distilling the dilute acidalcohol mixture resulting fromthe hydrolysis, this metlod of making tertiary alcohols employingsubstantially the same stepsas the ordinary method of making secondaryalcohols from oleiines.

It is preferred to carry out the purification ofsecondary from tertiaryalcohols according to the present invention at the time the alcohols aredistilled oft' from the acid-alcohol mixture after hydrolysis. In theaccompanying drawing I have illustrated diagrammatically a suitablearrangement of appa- Under these conditions Ewample By way of example,a. mixture of gases containing both secondary and tertiary olefines isintroduced into'the apparatus through the pipe 10. Pipe delivers gasespassing therethrough into the bottom of an absorber at 12. In theabsorber 12 the gases from pipe 10 are brought into intimate contactwith sulfuric acid to form alkyl sulfates from the secondary andtertiary oletines. Preferably the sulfuric acid is introduced 1nto theabsorber 12 at a relatively low temperature and passes through theabsorber countercurrent to the gases from pipe 10. Sulfuric acid can beconveniently introduced at a point such as Ithat indicated at 14 and amixture of alkyl sulfates or alkyl sulfates i and acidformed by theabsorption is removed from the lower part of the absorber 12 by a pipesuch as that indicated at 16. After the alkyl sulfates have been formedthey are diluted and hydrolyzed to form alcohols. For this purpose, pipe16 is connected to deliver the alkyl sulfates to a diluting andhydrolyzing tank 18. Water for diluting and hydrolyzing the alkylsulfates may conveniently be-introduced into tank 18 at a point such as20. After diluting the alkyl sulfates, hydrolysis is accomplishedpreferably in tank 18 in the manner well-known to those skilled in thisart to produce a mixture of alcohols and dilute acid. The dilute acidalcohol mixture is then distilled preferably in a lead lined still toseparate the alcohol from the acid. The hydrolysis may, if desired, beaccomplished simultaneously with the distillation of the' dilute alkylsulphates. For this purpose, the dilute alcohol-acid mixture is pumpedfrom the chamber 18 through the connecting line 22 to the lead linedstill 24. The dilute alcohol-acid mixture is heated in still 24 by anysuitable means, preferably Steam coils (not-shown) to drive olf thealcohols from the acid. Since the oleines introduced into scrubber 12contain some tertiary oleines as well as a predominati ng percentage ofsecondary olefines the alcohol vapors from still 24 contain sometertiary alcohols which it is rdesired to eliminate from the secondaryalcohols. The mixture of secondary and tertiary alcohol vapors leavingthe still 24 passes through dephlegmator 26 in which the alcohol vaporsare separated from any acid then entangled with the alcohols and frompart of the water vapors.

Preferably the tertiary alcohol is eliminated from the secondary alcoholsoon after the alcohol vapors leave the dephlegmator 26. For thispurpose, the mixture of tertiary and secondary alcohol vapors isconducted through pipe 28 to a series of dehydrating tubes 30, 30 whichare arranged in series and maintained at temperature conditions suitableto decompose the tertiary alcohols in the alcohol vapors. Preferably,the tubes 30 are maintained at a given constant temperature by an oilbath maintained in chamber 32 surrounding the tubes 30. In thearrangement illustrated the oil in thechamber 30 is heated to thedesired temperature by a burner 34, the hot gases of which act on a coil36 connected into a pipe 38 arranged to provide a circulation of the oilin the chamber 32. For this purpose, the pipe 38 is taken out of chamber32 at or near the bottom of the chamber and is carried back into chamber32 at or near the top of the chamber. A thermostat 40 is preferablyprovided in pipe 36 and arranged to control the fiow of gas to burner 34by means of a linkage 42 acting on a lever 44 of the gas valvle 46, soas vto maintain the oil in chamber 32 and thereby the tubes 30 at asubstantiallyl constant desired temperature. By controlling the amountof gas used by the burner 34, the temperature of the tubes 30 ismaintained constant and preferably at a temperature of about 250 C.Preferably, tubes 30 should aggregate over 20 feet in length. Theoptimum temperature of the tubes 3() will depend on whether or not acatalyst is used therein and upon the nature of the catalyst employed inthe tubes.

For any given catalyst, the 'temperature should preferably be such thatall of the tertiary alcohol is dehydrated to form tertiary olelines andwater, but without dehydrating or breaking down any material amount ofthe secondary alcohol. A catalyst of thoria carried on pumice is verysatisfactory when used in tubes 30 at atemperature of 250 C. Such acatalyst can be prepared in a variety of ways. A suitable method ofpreparing the said thoria-pumice catalyst is b mlxing thorium hydroxidewith pumice, rying the mixture and then heating it. method pumice may bevsaturated with a solution of thorium nitrate, dried and the nitratedecomposed by heat. A number of substances may be used as catalysts fordehydrating the tertiary alcohols, for example alumina, zirconia,aluminum sulfate, kaolin, and titania may be used in place of thoria.Moreover, the tertiary alcohols dissolved in commercial secondaryalcohol may be decomposed, although more slowly, by heat alone without acatalyst.

By another i The vapors leaving the catalyst tubes 30 are condensed andfor this purpose, the vapors from the last of the tubes 30 are conductedby pipe 48 into the coil of the condenser 50. The resulting condensateis a mixture of secondary alcohol and tertiar olefine. This mixture isconducted throng pipe 52 to a tank 54 in which the mixture fromcondenser 50 is heated under reiiux condenser 56. Condenser 56 permitsthe olefines to separate from the secondary alcohol and thetertiary-free secondary alcohol is there upon discharged from tank 54through pipe 58. The tertiary oleiine gases discharged from the refluxcondenser 56 through pipe 60 are substantially uncontaminated by otherthan tertiary material and may be utilized in a variety of ways.Preferably according to '2'0 the present invention tertiaryoleine gasesfrom pipe 60 are utilized as the source of commercially pure tertiaryalcohol. For this purpose, the pipe 60 is connected into the absorber 62forming part of an alcohol apparatus similar to that used in makingsecondary alcohols. In the absorber 62, the tertiary olefines areabsorbed in dilute sulfuric acid or other suitable acid reagent and theresulting tertiary alkyl sulfate hydrolyzed and distilled to formtertiary alcohol. In

the apparatus as illustrated, tertiary alkyl sulfate is discharged intoa diluting and hydrolyzing tank 64 from which the hydrolyzed mixture ofdilute acid and tertiary alcohol is pumped through pipe 66 into still68. The acid tertiary alcohol mixture is heated in still 68 to drive offalcohol vapors through a dephlegmator 70 and pipe 72 into the condensingcoil of a condenser 74 from which the commercially'pure tertiary alcoholis collected and conducted to storage.

Secondary alcohols which have been treated as just described give only aslight reaction when boiled with the Denige reagent, indicating thatremoval of thel tertiary alcohols has been substantially complete.

It Will be understood that, while the herein described process has beendeveloped and is particularly advantageous for removing tertiaryalcohols from secondary alcohols, its present invention is not limitedto use with secondary alcohols, but may be applied for the removal oftertiary alcohols from primary as well as from secondary alcohols.

Having thus described my invention, l claim:

1. The process of increasing the purity of alcohol containing tertiaryalcohol which comprises dehydrating said tertiary alcohol by heating thealcohol to a temperature of approximately 2500 C. to form oleiine andWater and removing said olefine from the alcohol.

2. The process of increasing the purity of alcohol containing tertiaryalcohol which comprises dehydrating said tertiary alcohol by heating thealcohol to a temperature of from 200 to 250 C. in the presence of acatalyst adapted to accelerate the dehydrating reaction to form olefneand waterand removing said oleline from the alcohol by distillation.

3. The process of increasing the purit of alcohol containing tertiaryalcohol w ich comprises dehydrating said tertiary alcohol by heating thealcohol to a temperature approximating 200o C. to form oleiine andWater, and removing said olefine from the alcohol by a reiluxing action.

4. The process of purifyin a secondary alcohol to remove tertiary alcooltherefrom, which comprises passing the impure secondary alcohol incontact with a dehydratin catalyst maintained at av temperature o about200 C., whereby the tertiary alcohol contained therein is decomposed andseparately recovering the purified secondary alcohol from thedecomposition products of the tertiar alcohol. l

5. T e process defined by claim 4 in which the said catalyst comprisesthoria.

6. The process defined by claim 4in which the said catalyst comprisesalumina.

7. The process dened by claim 4 in which the said catalyst compriseszirconia.

8. The com ined process of purifying secondary alcohols to removetertiary alcohols therefrom and to produce a relativel pure raw materialfor the manufacture o tertiary alcohols, which comprises heating theimpure secondary alcohols to a temperature of about 250 C. to therebyconvert the tertiary alcohols present to the corresponding olefines, andseparating the secondary alcohols from the decomposition products of thetertiary alcohols. n

9. The process definedby claim 8 in which said heating is conducted yinthe presence of a catalytic substance comprising alumina.

10. The process defined by claim 8 in which said heat is conducted inthe presence of a catalytic substance comprising zirconia;

11. The process defined by claim 8 in which said heat is conducted inthe presence of a catalytic substance comprising thoria.

12. A continuous process for purifying secondary alcohols to removetertiary alcohols therefrom, which comprises passing the impuresecondaryv alcohol in vapor phase through a heating zone maintained at atemperature adapted to decompose the tertiary alcohols present therein,but insufficiently high to decompose substantiall portions of the saidsecondary alcohols, sai temperature being maintained at a pointapproximating 250 C., and separately recovering the purilied secondaryalcohol and decomposition products of the tertiary alcohols.

13. The combined process of purifying an alcohol of its content oftertiary alcohol and simultaneously producing a relatively pure rawmaterial for the manufacture of tertiary alcohols, which comprisesselectively decomposing the tertiary alcohol in the impure alcohol byheating the impure alcohol to a temperature of about 200 C. Whilepassing it in Contact with a dehydrating catalyst adapted to acceleratethe decomposition of the tertiary alcohols to olefines, and separatelyrecovering the olefine decomposition product from the purified alcohol.

In testimony whereof I affix my signature.

ROBERT M. ISHAM.

